Petrels, Albatrosses, and Storm-Petrels of North America: A Photographic Guide

Summary

Petrels, albatrosses, and storm-petrels are among the most beautiful yet least known of all the world's birds, living their lives at sea far from the sight of most people. Largely colored in shades of gray, black, and white, these enigmatic and fast-flying seabirds can be hard to differentiate, particularly from a moving boat. Useful worldwide, not just in North America, this photographic guide is based on unrivaled field experience and combines insightful text and hundreds of full-color images to help you identify these remarkable birds.

The first book of its kind, this guide features an introduction that explains ocean habitats and the latest developments in taxonomy. Detailed species accounts describe key identification features such as flight manner, plumage variation related to age and molt, seasonal occurrence patterns, and migration routes. Species accounts are arranged into groups helpful for field identification, and an overview of unique identification challenges is provided for each group. The guide also includes distribution maps for regularly occurring species as well as a bibliography, glossary, and appendixes.

The first state-of-the-art photographic guide to these enigmatic seabirds
Includes hundreds of full-color photos throughout
Features detailed species accounts that describe flight, plumage, distribution, and more
Provides overviews of ocean habitats, taxonomy, and conservation
Offers tips on how to observe and identify birds at sea

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INTRODUCTION

WHAT ARE TUBENOSES?

In traditional classifications such as that of the American Ornithologists’ Union (AOU) (1998), tubenoses are a well-defined group of seabirds that comprise the order Procellariiformes, and are so-named because their nostrils are encased in tube-like structures on the bill. Tubenoses are represented by up to five families worldwide: northern storm-petrels, southern storm-petrels, albatrosses, petrels (including shearwaters), and diving-petrels (a southern hemisphere family not covered in this guide, and sometimes merged with the petrels). Based upon DNA studies, Sibley and Monroe (1990) treated all of the tubenoses as a single family (Procellariidae) within the superfamily Procellarioidea, which also includes frigatebirds, penguins, and loons.

Tubenoses occur all over the world’s oceans and vary in appearance from the tiny, swallow-like storm-petrels to the great albatrosses, among the largest of flying birds, with wingspans approaching 3.5 m (almost 12 feet)! Wings range from relatively broad and rounded in some storm-petrels to long, narrow, and pointed in the majority of species. Tails mostly range from squared to graduated, but several storm-petrels have forked tails. All tubenoses have 10 functional primaries and most have 12 rectrices (fulmars have 14, giant-petrels 16); the number of secondaries ranges from 11–13 in storm-petrels to 25–38 in albatrosses.

Bills vary from fairly short in storm-petrels to long and substantial in albatrosses, and all have hooked tips and are covered by distinct horny plates. The nostrils of albatrosses are mounted in small tubes on either side of the bill, whereas in petrels and storm-petrels they are fused into a tube on top of the bill base (Figs 1–2). Tubenoses drink saltwater and excrete surplus salt in solutions that leak out of the nostril tubes. All species have short legs and webbed feet, with the hind toe absent (in albatrosses) to greatly reduced (in petrels and storm-petrels); the toes of burrowing species in particular have strong and sharp claws. Tubenoses have a well-developed olfactory bulb and use smell to find food and help locate their burrows in the dark (the plumage of most petrels and storm-petrels has a distinctive musky odor, which pervades their nests). It has even been found that adults of some species can distinguish by smell their own burrows from those of their neighbors (Bonadonna et al. 2003).

Fig 1. On albatrosses, such as this Black-footed Albatross, the nostril tubes lie on either side of the bill (cf. Fig 2). SNGH. Off Bodega Bay, California, 14 Aug 2007.

Fig 2. On petrels, such as this Sooty Shearwater, the nostrils open in a double-barreled tube at the base of the culmen (cf. Fig 1). SNGH. Off Monterey, California, 11 May 2008.

The plumage of tubenoses is dense and waterproof, hued in blacks, grays, browns, and whites. Some species are all-dark whereas others are strikingly patterned, with contrasting white uppertail coverts (as in some storm-petrels) or bold underwing markings (as in some petrels). The bills of most smaller species are black or dark, but some larger species, especially albatrosses, have brightly colored bills; the legs and feet of most species are blackish or pinkish overall.

Sexes appear alike in plumage although in some of the large albatrosses males more quickly develop adult plumage—a male Snowy [Wandering] Albatross 5 years old may be as white as a female 20 years old (Prince et al. 1997). In general, males average larger in albatrosses and petrels, whereas females average larger in storm-petrels. This is rarely apparent at sea except perhaps in bill depth or, with some albatrosses, in the bulk and width of the head (females having more slender heads). In most species the fledglings appear indistinguishable from adults, which is something to be thankful for in terms of at-sea identification. Appreciable age-related variation in appearance is largely limited to albatrosses. Molt in tubenoses is relatively poorly known. Most tubenoses do not molt their wings while breeding, and the time available for molt can be as little as a few months between successive breeding seasons. Thus, particularly among albatrosses, molt can involve novel strategies that allow the maximum number of primaries to be replaced in a short period. As adults, all tubenoses have one molt per cycle (a cycle for most species being a year), which, especially in larger species, is often incomplete, with not all remiges being replaced in a single cycle (see Molts, Plumages, and Aging, pp. 38–45). Because flight is so important to tubenoses, some species will skip a year of breeding to catch up on their molt rather than risk another season with impaired flight capabilities.

Except for the diving-petrels, which have sacrificed wing area to allow them to dive better (like northern hemisphere auks), tubenoses are generally accomplished fliers—as they have to be to live in such an open and windy environment (see Flight Manner, pp. 24–28). All rest on the sea surface, and many species dive well for food (especially shearwaters). Most tubenoses are migratory to some degree. These migrations vary from poorly understood shorter-distance dispersals to spectacular transequatorial odysseys.

Life at sea is all about finding food, which is patchy, mobile, and unpredictable (see Ocean Habitats, pp. 5–13). Tubenoses can survive fairly long periods without feeding and have a great ability to lay down subdermal fat for insulation, which helps them through fasting periods such as incubation (spells of which can last 3–4 weeks in albatrosses). Tubenoses find their food by sight and smell, and they forage by day and night (some food items perform vertical migrations, and only approach the surface at night); the main food groups are squid, fish, and crustaceans such as krill. Feeding strategies include scavenging, seizing prey near the surface, diving to depths of 50 m or more, and even pirating other species. Scavenging is a common form of feeding for many tubenoses, such as Tahiti Petrel and storm-petrels (Fig 3). This is why fish-oil slicks (which mimic dead fish) are successful in attracting certain tubenoses, notably petrels and storm-petrels, which can detect smells from miles away. Some fishing operations, mainly in productive temperate waters, provide large quantities of offal. Albatrosses and fulmars can gather in hundreds or even thousands to eagerly consume this free food (free in the myopic, human short term). In fact, the best way to find albatrosses in some areas is to locate active fishing boats. However, the practice of setting baited hooks (such as the thousands used by long-line fishing operations) without protecting them from hungry tubenoses causes countless birds to take the bait and drown—a major source of mortality for some species, particularly albatrosses, and a serious conservation issue that is beginning to be addressed.

Fig 3. Many species of tubenoses, here a Black-capped Petrel and a Wilson’s Storm-Petrel, scavenge dead squid and fish, which can be detected from miles away courtesy of an acute sense of smell. SNGH. Off Hatteras, North Carolina, 15 Aug 2009.

Fig 4. Pink-footed Shearwaters over Humpback Whale. Several species of petrels feed in association with whales and dolphins, presumably scavenging spillage and scraps. SNGH. Off Monterey, California, 26 Sep 2008.

In tropical waters, schools of dolphin and tuna chase schools of fish to the surface, allowing many tubenoses to feed on the smaller fish being pursued as well as on left-over scraps. For example, Juan Fernandez Petrels and Wedge-tailed Shearwaters (along with Sooty Terns and numerous other species) feed over yellowfin tuna in the tropical Pacific Ocean (Spear et al. 2007), Parkinson’s Petrels often scavenge in association with dolphins off Middle America (Pitman & Ballance 1992), and Pink-footed Shearwaters often forage over whales or schools of dolphins off California (pers. obs.; Fig 4).

All tubenoses nest on or under ground, typically on islands that are (or were) free from predators, and most species are colonial. Long-distance migrants and species breeding at high latitudes tend to be more synchronized in their breeding, whereas tropical species and shorter-distance migrants tend to have more protracted and less synchronized cycles. A high degree of philopatry characterizes tubenoses, and young birds generally return to their natal islands for breeding; when breeding islands are at carrying capacity, however, young birds may range widely in search of suitable new breeding sites. Larger species such as albatrosses and fulmars are diurnal at the breeding grounds and nest on the surface, whereas most smaller species are nocturnal and nest in burrows or crevices, coming and going at night to avoid predators such as hawks, falcons, gulls, and skuas.

The ocean is not a gentle or forgiving mother, and tubenoses need to know what they’re doing before they start breeding. All species have a conservative reproductive strategy characterized by late maturity, low reproductive rates, and long life spans. The typical age of first breeding in tubenoses ranges from 4–5 years in storm-petrels to 6–13 years in albatrosses, some of which can live for 50 or more years. Prebreeding birds visit colonies for a few years before settling, and arrive earlier each year as they get older to develop long-lasting monogamous pair bonds. Breeders usually return at least one or two months before egg-laying, to bond with their mates and refurbish the nest site. A prelaying exodus, or honeymoon period, when birds leave the nesting grounds for 2–4 weeks, is characteristic of tubenoses and most apparent in species with synchronized breeding systems. During this time the egg is developed and birds store food reserves for incubation spells. Incubation for the single white egg ranges from about 6–8 weeks in storm-petrels to 9–11 weeks in albatrosses. Fledging requires from around 7–10 weeks in storm petrels to 20–40 weeks in albatrosses, and nestlings are adapted to survive weeks without food while their parents roam the oceans. In the largest albatrosses, more than a year is required for a breeding cycle and so these birds only breed every other year. Hybrid tubenoses—derived from two species interbreeding—appear to be very rare, and the only well-documented ones that occur in the region are those between Black-footed and Laysan albatrosses (Fig 5). Even so, these are sufficiently rare that most birders will never see one.

The voices of tubenoses are unmusical and heard mostly at or near the breeding grounds. They comprise a variety of brays, whinnies, purring chatters, whistles, moans, and sometimes other-worldly shrieks and screams. Periods of loud calling over storm-petrel colonies in the middle of the season, after laying or hatching, may be due largely to the presence of prebreeding immatures. Calls, in conjunction with ritualized display postures and bouts of bill-clapping in some species, serve important social functions during courtship, territorial disputes, and arguments over food. Calls are of limited value for identification except at night on the breeding grounds when, e.g., they enable different species of storm-petrels to be distinguished. An excellent reference to the sounds of tubenoses in the Northeast Atlantic is the Sound Approach guide by Magnus Robb and colleagues (Robb et al. 2008).

OCEAN HABITATS

As with all birds, habitat is a key to understanding patterns of distribution and occurrence. We all readily recognize grasslands, marshes, conifer forests, and such on land, but what of marine habitats? The oceans are not simply wet and salty but instead they comprise many habitats usually invisible to the human eye (Figs 6–7). On land, these habitats would be as different as deserts are from rainforests, and at sea they are mobile deserts and rainforests! Both large-scale and small-scale physical processes in the ocean can change the habitat in an area overnight, as many people who have taken pelagic trips on two consecutive days to the same area can attest. We are a long way from understanding, let alone predicting, many of the large-scale, let alone small-scale, changes to which seabirds respond. The following is a simplified overview of the oceans as they relate to habitat for seabirds, particularly tubenoses.

Current Systems (Fig 8a–8b)

Oceans and seas are the contiguous saltwater masses that cover about 70% of the Earth’s surface. They surround and define land masses and are dynamic water bodies within which patterns of predictable circulation can be identified at different depths. Ocean currents are the dominant feature of surface movement and they broadly correspond to the direction of prevailing winds, which themselves are a consequence of the easterly direction of the Earth’s rotation, solar heating, and the torque of the Coriolis force.

This means that at the large scale of ocean basins the prevailing winds (and currents) are easterly (flowing from east to west) in tropical latitudes, westerly in mid-temperate latitudes, and easterly again at high latitudes. Conversely, the continental coasts have an overall north-south orientation. Thus, in the Americas, westward-flowing equatorial currents driven by the easterly Trade Winds push water away from Pacific coasts but toward Atlantic coasts, whereas eastward-flowing mid-latitude currents driven by prevailing westerly winds push water toward Pacific coasts and away from Atlantic coasts.

The Coriolis force lends a clockwise direction to mid-latitude water mass circulations in the northern hemisphere and a counterclockwise direction in the southern hemisphere. Consequently, in low to mid-latitudes there is a flow of relatively cold, higher-latitude water toward the equator along the eastern edges of the oceans, forming eastern boundary currents such as the California Current and Humboldt (or Peru) Current. Conversely, relatively warm tropical water flows away from the equator along the western edges of the oceans, forming western boundary currents such as the Gulf Stream and Kuroshio Current. At high latitudes, the current patterns reverse with the reversal of prevailing winds, and relatively warm water flows north into the Gulf of Alaska as the Alaska Current, while cold water flows south from the Davis Strait as the Labrador Current. To maintain equilibrium (all of the westward-flowing tropical water has to be replaced somehow), roughly along the equator there is an eastward-flowing current (the Equatorial Counter Current) that transports water back across the oceans between the North Equatorial and South Equatorial currents.

In addition to these major current systems there are numerous smaller-scale currents. In the Pacific, e.g., on reaching the American mainland the Equatorial Counter Current splits into the relatively warm, and usually weak, north-flowing Costa Rica Current and the south-flowing, somewhat submerged Peru Undercurrent. In the North Pacific, the Alaska Current curves around to form a westward-flowing current along the south side of the Aleutians, but some water splits off to enter the eastern Bering Sea (through Unimak Pass) and circulate in a clockwise gyre over the continental shelf.

The inherently dynamic nature of ocean water masses means that currents vary in their strength and position (even on a daily basis), but the broad patterns are consistent and helpful to have in mind when considering seabird distribution.

Thermoclines, Upwelling, and Fronts

The oceans are not uniform in nature, and within them we can distinguish distinct water masses by characteristics such as their density, which is a product of temperature and salinity. Temperature is the feature most easily appreciated by humans, although salinity may be more important in defining habitats for marine organisms. The bottom line is that the interactions of different water masses affect biological productivity. When organisms in the sea die they sink, taking the nutrients needed for photosynthesis into the cooler, deeper ocean waters. But photosynthesis can occur only in surface waters to the depth of sunlight penetration. Thus biological productivity depends in part on forces that bring nutrient-rich cooler waters into the zone where photosynthesis can occur.

Fig 8a–8b. An overview of ocean currents relating to North American waters (warm, neutral, and cold are relative terms for the prevailing currents). At mid-latitudes, warm currents such as the Gulf Stream flow away from the equator along eastern coasts, whereas cold currents, such as the California Current, flow toward the equator along western coasts.

Thermoclines. Productivity can often be inferred by looking at the nature of the temperature gradient between warmer surface waters and cooler subsurface waters, which is called a thermocline. This gradient may be abrupt (a strong thermocline) or diffuse (a weak thermocline), and it can be nearer to (shallow) or farther from (deep) the sea surface.

For example, strong, deep thermoclines indicate little mixing of the cooler, nutrient-rich subsurface waters with the warmer, nutrient-poor surface waters. Ocean areas with these characteristics tend to be biologically unproductive, like the vast areas of blue water in the tropical and subtropical Central Atlantic and Central Pacific oceans, which are effectively marine deserts. Some species, such as Bulwer’s Petrel, seem adapted to roam these deserts in search of food, but in general such areas are poor in seabird life. The much-publicized El Niño events that cause periodic food-web crashes in the Humboldt and California currents occur when the thermocline deepens; this happens when the Trade Winds slacken, which allows warm surface water that has been pushed to the western Pacific to slop back to the east and intrude over cooler water masses.

Weak and shallow thermoclines, on the other hand, indicate mixing of water masses, so that nutrients and sunlight combine. Hence there is increased food productivity, which extends through the food web to seabirds. Such mixing occurs where cool subsurface waters are drawn toward the surface (or upwelled) and where different water masses meet (at fronts).

Upwelling can occur in a number of ways. For example, where surface waters have a tendency to diverge, the space thus created may be filled by upwelling of cooler subsurface waters. Waters along the equator are relatively cool for this reason, because the Trade Winds driven by the Coriolis force tend to push the surface water north and south away from the equator. Upwelling also occurs when subsurface currents hit rises in the seafloor and are forced upward, so that nutrient-rich waters may be pushed into the sunlight zone, e.g., over seamounts, submarine canyon walls, and the continental shelf break. Tidally induced currents can also contribute significantly to upwelling among islands and over continental shelf waters, such as at Georges Bank, between Cape Cod and Nova Scotia, and in Hecate Strait, inshore of the Queen Charlotte Islands off British Columbia, where large numbers of Sooty Shearwaters gather to molt (Fig 9).

The best-known types of upwelling are the wind-driven systems associated with eastern boundary currents such as the California and Humboldt currents, which are rich feeding grounds for seabirds. But even in these areas productivity is cyclic because wind direction and strength vary, often on a seasonal basis. Upwelling can be greatly suppressed if the prevailing winds simply aren’t blowing, but then even a day or two of strong winds can generate significant upwelling.

The frictional drag of wind on the ocean surface, combined with the Coriolis force, means that water flows at an angle to the wind direction: water angles to the right in the northern hemisphere, to the left in the southern hemisphere. Thus, in spring and summer (mainly March to August) the prevailing northwest winds along the Pacific coast from Oregon to California cause surface water to flow to the right, or offshore, and cool subsurface water upwells at the coast to take its place before being similarly conveyed offshore. Two other areas of seasonal Pacific coastal upwelling in North America are around the Gulf of Tehuantepec, in southern Mexico (mainly October to March), and in the Gulf of Panama (mainly January to April), where strong winds funnel across the land isthmuses from the Gulf of Mexico and Caribbean; large numbers of Black and Least storm-petrels occur in both areas at these seasons. During El Niño events the deepened thermocline means that warm, nutrient-depleted water upwells instead of cold water, and marine productivity is greatly reduced even with upwelling.

Fronts represent the meeting of different water masses. They are three-dimensional systems, and the depth to which they extend in the water column varies with their scale and with local conditions. They can be large scale, as between the Labrador Current and Gulf Stream (Fig 10), or small scale, such as the passes between some Aleutian Islands where North Pacific and Bering Sea water masses are mixed by tidal-current action that also promotes local upwelling; many Short-tailed Shearwaters gather to molt in these productive areas.

Fig 10. Few ocean fronts are as abrupt as the break between the cold green Labrador Current (at back, around 5°C) and the warm blue Gulf Stream (in front, around 16°C and warming rapidly away from the front). Food items, and thus birds (such as these Dovekies Alle alle), often concentrate along such fronts. SNGH. Off Hatteras, North Carolina, 14 Feb 2010.

The relatively shallow waters over the continental shelf usually differ from deeper offshore waters in temperature and salinity (e.g., shelf waters are fed by freshwater runoff from land and are mixed more by tidal action); these water masses meet and mix at what are known as shelf-break fronts, areas of generally high productivity. Upwelling fronts occur when cool, upwelled water flowing offshore sinks where it meets warmer, less dense water; plankton are usually concentrated at upwelling fronts, which are often good for birds. The shelf-break front and upwelling fronts often lie over the continental shelf break, where current-driven upwelling can further enhance productivity—so it is not surprising that the shelf break is usually a good area for seabirds and seabirding.

Fig 11. Sargassum weed and associated tubenose prey items concentrate at fronts between different water masses along the edges of the Gulf Stream. SNGH. Off Hatteras, North Carolina, 26 May 2007.

Other, usually short-lived, fronts are the locally wind-driven or tidally driven convergences marked by strips of glassy, slick-like water dotted with lines of debris and weed (Fig 11), among which are fish eggs, gelatinous zooplankton, and other biological matter. Off California in fall these small-scale fronts often attract Buller’s and other shearwaters, phalaropes, Long-tailed Jaegers, and Xantus’ Murrelets. Off the southeastern U.S. in summer they are good areas to find Audubon’s and other shearwaters, and Bridled and other terns. Internal waves (subsurface waves that generate vertical undulations in the thermocline) are another physical phenomenon that helps explain the small-scale patchiness of seabirds within larger-scale water masses, as noted for Black-capped Petrels off the southeastern U.S. (Haney 1987a).

Habitat Associations

For tubenoses, at-sea habitat translates largely to food. But food in the oceans is not evenly spread, and it is also dynamic in its distribution: trying to predict details of tubenose distribution patterns at sea is a little like trying to predict exactly when and where it will rain. Still, as with climatic zones on land, broad-scale marine habitat zones can be identified. Characteristics of marine habitats are rather different from those we associate with habitats on land, and include sea-surface temperature and salinity, thermocline depth and strength, ocean depth (such as over or offshore of the continental shelf), and even wind strength and wind direction. For example, albatrosses need sufficient wind speeds to support their flight, and they avoid areas with persistently low winds or calm conditions.

Within broader-scale habitats there are hotspots that concentrate food and are favored by seabirds, and by birders. For example, in the Cordell Bank National Marine Sanctuary, off the central California coast, the outer boundary of the wind-driven upwelling system corresponds with the shelf-break front and is enhanced by tidally induced and subsurface current upwellings; this all results in a productive area where 25 species of tubenoses, including 5 albatrosses, have been recorded.

As with terrestrial habitats, the avifaunas of marine habitats vary seasonally. The California Current system is a well-studied example. In spring and summer, persistent northwest winds from Oregon to central California drive the upwelling of cool, nutrient-rich, south-flowing waters that support a large avifauna of locally breeding and migrant seabirds. With changing atmospheric conditions in fall, the northwest winds decrease in both strength and persistence, the upwelling productivity is reduced, and warmer oceanic water moves onshore (mainly during August to October, when several warmer-water seabirds expand their ranges northward). The winter climate that follows is characterized by southerly winds, which allow the relatively warm, northward-flowing, and usually subsurface Davidson Current to dominate inshore marine waters during November to March (when productivity is reduced and fewer tubenoses occur), before the northwest winds return in spring.

Different habitats show varying degrees of overlap. In the Pacific Ocean, Wahl et al. (1989) found that the high-temperature/high-salinity avifauna of the subtropical North Pacific overlapped little with the three colder water/lower-salinity avifaunas to the north and east, which had numerous species in common. Habitats can also be interpreted differently. For example, Gould and Piatt (1993) recognized 3 avifaunas (comprising 14 species guilds) within the 2 offshore North Pacific avifaunas identified by Wahl et al. (1989). Tables 3–4 list the broad-scale distribution of tubenose avifaunas in North American waters during spring to fall.

The habitats described above help explain seabird distributions as we see them today. But environments are nothing if not dynamic, and a longer-term view of tubenose distributions is also of interest in understanding present-day patterns and perhaps in predicting future trends. The origins of tubenoses are shrouded in the mists of prehistoric time, but different lines of evidence agree on a common ancestor for penguins, tubenoses, and loons (Cracraft 1981, Olson 1985, Sibley & Alquist 1990). The fossil record also indicates that the tubenose families recognized today were distinct some 30 million years ago, and that most modern genera existed around 10 million years ago (Brooke 2004).

The times and rates of evolution for different groups of tubenoses are contentious, but the order likely originated in the southern hemisphere along the shores of a fragmenting Gondwanaland. It appears that storm-petrels split first from the ancestral tubenose lineage, followed by the albatrosses, and then the ancestor of petrels and diving-petrels, with the diving-petrels having diverged relatively recently (Harper 1978, Nunn & Stanley 1998; Fig 12).

Until much more work is undertaken, unraveling the geographic origins of different families and genera of tubenoses will remain controversial. Islands and shores of the proto-Pacific Ocean seem likely candidates, however, given that the Indian Ocean and Atlantic Ocean did not open up until the plates of Gondwanaland diverged. Certainly, the modern-day breeding distributions of tubenoses are heavily weighted to the Pacific and to the southern hemisphere. Tubenoses, however, are tied to oceanic habitats, not to land, and their present-day breeding distributions may simply reflect the nearest predator-free land masses as much as any biogeographic ties to the immediately surrounding seas.

Tubenose distributions are ever-changing over different time scales, and what we see today are relics of a richer, more diverse bygone era. For example, the fossil record indicates that around 2–4 million years ago up to five species of albatrosses roamed the North Atlantic, where none is regular today, and there was even a breeding population of Steller’s Albatrosses on Bermuda! (Olson & Rasmussen 2001). Even in our lifetimes we can see changes. For example, Northern Fulmars and Manx Shearwaters spread across the North Atlantic from western Europe to North America in the 1960s and 1970s and, as I write this, Manx Shearwaters appear to be colonizing the North Pacific. Laysan Albatrosses have colonized islands off west Mexico since the 1980s, apparently because their Hawaiian nesting grounds reached carrying capacity so that young were forced to roam in search of new lands. Given the strong philopatry of breeding adult tubenoses, the pioneering movements of young birds have likely resulted in range shifts and expansions. New colonizations need not always be driven by increasing populations: steadily rising sea levels during past eras would have reduced the area of nesting grounds and caused a steady shift in breeding distributions (or extinctions, if no alternative breeding sites could be found). Something similar may be happening today on islands where burgeoning fur seal populations appear to be limiting albatross nesting sites (such as of Snowy [Wandering] Albatross on South Georgia, and of Salvin’s Albatross on the Bounty Islands).

The occurrences of vagrant tubenoses visiting islands beyond their breeding range are noteworthy events in the birding world, but might some be precursors of range changes that will span thousands of years? Could they be inexorable responses to climatic change? Or are they simply random events? Examples include Black-browed Albatross and Barolo Shearwater in Britain, Wedge-rumped Storm-Petrel and Cory’s Shearwater off Baja California, Mexico, Salvin’s Albatross in Hawaii, Trinidade Petrel in the West Indies, and Bermuda Petrel in the Azores.

Of the 70 or so tubenose species recorded in North America, only 16 breed in the region covered in this guide; about 36 are regular or probably regular nonbreeding visitors (some occurring in only very small numbers) from breeding grounds as distant as Hawaii, Japan, Australia, New Zealand, Chile, Antarctica, Europe, and the South Atlantic; and about 17 appear to be vagrants. Most vagrants originate from habitats similar to those found in the region: 12 species (9 albatrosses, 2 petrels, 1 storm-petrel) come from temperate and subtropical latitudes of the southern hemisphere, whereas only 5 species (1 albatross, 2 petrels, 2 storm-petrels) come from tropical regions and subtropical northern latitudes adjacent to the region. Thus, in temperate waters off California you are more likely to encounter species of temperate southern hemisphere waters (such as Gray-faced [Great-winged] Petrel) than to find species that occur much closer but over tropical and subtropical waters (such as Kermadec Petrel).

TAXONOMY AND AN IDENTIFICATION FRAMEWORK

Taxonomy is the science of classification and it allows us to place birds within a frame of reference. Birds, like all living organisms, are classified by a hierarchal system. The category most familiar to birders is that of a species, and an important category just above the species level is the genus; a subgenus is a grouping between the levels of genus and species. Each genus (and subgenus) has certain shared characteristics, an appreciation of which can be helpful in identification. For example, Leach’s Storm-Petrel, like other members of the genus Oceanodroma, has relatively narrow and angled wings with a long arm, whereas Wilson’s Storm-Petrel, like other members of the genus Oceanites, has relatively broad-based and straight wings with a short arm.

Each described organism on Earth has a scientific name, which is italicized and comprises its genus name (capitalized) and species name (lowercase). Variation within a species, if noticeable and correlated with geographic populations, may be expressed by means of subspecies (also called races); species with recognized subspecies are termed polytypic. A species is monotypic if no subspecies are recognized. A subspecies name is the third and last part (also termed an epithet, or trinomial) of the scientific name. With few exceptions, the first-described population retains the same subspecies epithet as the species epithet, and is known as the nominate subspecies. For example, the nominate subspecies of Northern Fulmar is Fulmarus glacialis glacialis (often abbreviated to Fulmarus g. glacialis), which breeds in the North Atlantic, while the subspecies Fulmarus glacialis rodgersii breeds in the North Pacific and can be classified as:

Class: Aves

Order: Procellariiformes

Family: Procellariidae

Genus: Fulmarus

Species: glacialis

Subspecies: rodgersii

The classification of tubenoses has followed a long and tortuous path, with much debate about whether separate populations are species or subspecies. Many taxa, populations, or even color morphs were originally described as separate species. A conservative period followed, with some rather extreme lumping based largely on philosophical grounds rather than new data. Thus, e.g., Murphy (1952) subsumed eight taxa of shearwaters as one, the Manx Shearwater (all eight are now considered full species again).

Like all traditional classifications, that of tubenoses has relied heavily on plumage patterns and external morphology. Recent genetic studies have repeatedly shown, however, that some taxa may diverge yet show little external evidence of their genetic separation, whereas distantly related taxa can converge in appearance and morphology. An example of the former situation occurs with different populations of Band-rumped Storm-Petrel, which may comprise as many as 10 species worldwide, with 4 in the northeastern Atlantic alone (Robb et al. 2008). An excellent example of the latter situation is the Little Shearwater/Audubon’s Shearwater complex, which traditionally has been considered to comprise two widespread but rather variable species: the higher-latitude Little Shearwater, with a shorter tail and white undertail coverts, and the lower-latitude Audubon’s Shearwater, with a longer tail and dark undertail coverts. Austin et al. (2004) showed that this complex comprises multiple species, and that one population of Little Shearwater from the North Atlantic is actually an Audubon’s Shearwater! An interesting parallel in morphological variation occurs in the Manx Shearwater complex, such as between the higher-latitude Manx (with a shorter tail and white undertail coverts) and the lower-latitude Townsend’s Shearwater (with a longer tail and dark undertail coverts).

As well as finding that traditional morphology does not necessarily reflect relationships, genetic studies have revealed a trend for geographic clades, whereby a presumed ancestor colonized an area and then diversified. Examples include the North Pacific clade of Phoebastria albatrosses, and the North Atlantic clade comprising Audubon’s, Boyd’s, and Barolo shearwaters, with the last-named resembling the southern hemisphere Little Shearwater complex (Austin et al. 2004). A further complication is that specimens may look similar in a museum tray whereas the birds in life (and genetically) are quite different. An example is the Fea’s Petrel complex, which is part of a North Atlantic clade (including Black-capped and Bermuda petrels) and not closely related to the southern hemisphere Soft-plumaged Petrel (Nunn & Stanley 1998), with which Fea’s was lumped for many years based on superficial similarities.

As new information becomes available, subspecies are being elevated to species rank (such as Hawaiian and Galapagos petrels; AOU 2002), cryptic species are being identified (such as Henderson Petrel; Brooke & Rowe 1996), and some distinct taxa even remain to be named (such as Grant’s [Band-rumped] Storm-Petrel). Thus, taxonomy within the tubenoses remains dynamic—and often controversial, such as proposals to elevate all albatross taxa to the level of species. In birds as site-faithful as albatrosses every island population could, in theory, evolve into a species: witness the coexistence of Desertas [Fea’s] and Zino’s petrels in the Madeira archipelago, and the differences found among populations of Galapagos Petrels from different islands in the Galapagos archipelago (Tomkins & Milne 1991). The difficulty, for humans, lies in determining how differentiated insular populations have become—which should be recognized as species and which should not?

Despite the state of flux in tubenose taxonomy and nomenclature, the classification of the American Ornithologists’ Union Checklist of North American Birds (and subsequent supplements) is particularly anachronistic and is not followed here. Instead, I have tried to pick a realistic course through various taxonomic papers (Austin 1996, Austin et al. 2004, Chambers et al. 2009, Harper 1978, Imber 1985, Nunn & Stanley 1998, Viot et al. 1993), but I acknowledge the fluid state of tubenose taxonomy. One recent review of taxonomy and nomenclature in tubenoses as a whole (Penhallurick & Wink 2004) contained numerous flaws (Rheindt & Austin 2005) and has not been generally accepted. Another review (Kennedy & Page 2002) represented an exercise in statistics more than an advance in taxonomy.

Tubenoses have been traditionally divided into four families: albatrosses, petrels, diving-petrels, and storm-petrels (Figs 13–15). Recent studies, however, suggest it is more realistic to treat diving-petrels as a subfamily within petrels, and to consider storm-petrels as two families (see Fig 12). Some features of each genus or subgenus within these families are described below (at least for species recorded in North America). In the species accounts these families and genera are subdivided into groups convenient for field identification, which do not necessarily reflect taxonomic relationships.

Fig 13. Black-footed Albatross and Chapman’s [Leach’s] Storm-Petrel are examples of the larger and smaller tubenoses; both scavenge together at squid and fish carcasses. SNGH. Off San Diego, California, 25 Aug 2009.

Fig 14. Although large for a petrel, this Pink-footed Shearwater is dwarfed by a Black-footed Albatross (an adult with extensively white uppertail coverts), which is relatively small for an albatross. SNGH. Off Monterey, California, 21 Sep 2007.

Fig 15. The small size of Wilson’s Storm-Petrel is readily appreciated with a Cory’s Shearwater for scale. SNGH. Off Hatteras, North Carolina, 31 May 2007.

Family Procellariidae: Petrels

Petrels, which include shearwaters, are a well-defined family of tubenoses, but over the years they have been divided into many different groups by different authors. There is increasing agreement that both the fulmar clade (represented in the northern hemisphere by one species, with six other species in five genera inhabiting the cold Southern Ocean) and the Pterodroma clade are distinct monophyletic groups. Other relationships are less clear, including those of the shearwaters and the genera Procellaria, Bulweria, and Pseudobulweria (as well as of some southern hemisphere genera unrecorded in North America). Genetic studies confirm that the traditional Puffinus shearwaters are not monophyletic (Austin 1996, Nunn & Stanley 1998). Thus the larger Puffinusshearwaters are treated here in the genus Ardenna, with Puffinus reserved for the smaller shearwaters, which share a common ancestor with Calonectris. Fig 16 shows a provisional phylogeny of present-day petrel genera recorded in North America. The following genera occur in North American waters, listed here in the sequence of three main groups used for identification (shearwaters, gadfly petrels, and other petrels).

Shearwaters comprise three genera worldwide, all found in the region: Ardenna, Calonectris, and Puffinus. Gadfly petrels in the region comprise two genera: Pterodroma and Pseudobulweria. Other petrels in the region involve three genera: Fulmarus, Procellaria, and Bulweria.

Genus Ardenna. Seven species of large shearwaters, all of which occur in the region; six breed in the southern hemisphere and migrate to the northern hemisphere to molt, and one (Wedge-tailed) breeds and ranges in the tropics. This genus might best be considered as multiple genera, but it is recognized here provisionally to highlight that these large shearwaters are not closely related to true Puffinus. Bills are relatively slender, varying from blackish to pink with a black tip, and legs and feet are pink to dusky overall. Plumage is all-dark or bicolored. Wedge-tailed and Buller’s are a distinctive pair that can be recognized in the subgenus Thyellodroma, differing from other species in lighter build, relatively broader wings, and longer, strongly graduated tails, which combine to give them a buoyant flight manner befitting their lower-latitude distribution. Typical Ardenna are heavier bodied with shorter tails and narrower and stiffer wings, and inhabit higher latitudes with stronger winds. For species identification note flight manner, overall plumage pattern, tail shape, head and neck patterns, bill color and size, and underwing pattern.

Genus Calonectris. Four species (all recorded in the region) of large shearwaters with long and overall pale bills, broad wings, and medium-long graduated tails. All breed in warm subtropical waters of the northern hemisphere and further differ from Ardenna in having longer and heavier bills, rounded tarsi, lighter skeletons, and more marked sexual dimorphism (male bills being 5–13% longer than those of females). For species identification check head and neck pattern, bill color, and underwing pattern.

Genus Puffinus. At least 26 species (taxonomy is vexed) of small to very small shearwaters. That only eight species have been recorded in the region reflects the relatively sedentary habits of many taxa. Puffinus shearwaters are widespread in tropical and mid-latitudes. Most species are bicolored, dark above and white below, although two are dark overall, including Christmas Shearwater, which traditionally has been associated with the larger shearwaters. Bills are dark overall, and legs and feet mostly pinkish to pale bluish. Similarities in plumage patterns have clouded the determination of species limits, and it is likely that more species await recognition, or even formal discovery. For species identification note overall structure (especially tail length), head and neck pattern, undertail-covert pattern, underwing pattern, and bill size.

Genus Pterodroma. Approximately 30 species (taxonomy is vexed) widespread in tropical and subtropical latitudes. They are often simply called pterodromas in birding talk, or known as gadfly petrels because of their impetuous flight manner. In North American waters at least 15 species of gadfly petrels have been recorded. Gadflies are small to medium-sized petrels that range from all-dark to bicolored, with dark upperparts and white underparts; the upperparts of several species have a blacker M pattern. The bills are black, notably stout on larger species but relatively slender on some of the smaller species; the wings are generally long, relatively narrow, and pointed, characteristically held pressed slightly forward, crooked at the carpals, and flexed; the tails are slightly to distinctly graduated, varying from medium-short and relatively squared to medium-long and tapered; the toes do not project in flight and usually the feet are hidden in the plush undertail coverts; legs and feet vary from all-dark to pale pinkish or pale bluish with black distal toes and webbing. The genus may include multiple genera, but data are not available to resolve relationships for all species. For species identification note overall size (small, medium, or large), head and neck pattern, underwing pattern, flight manner, and bill size.

Genus Pseudobulweria. Four or more poorly known tropical species of medium-sized petrels with very stout black bills, long wings, and medium-long graduated tails. One distinctive species (Tahiti Petrel) occurs in the region and has very long narrow wings and overall dark plumage with a contrasting white belly and undertail coverts.

Genus Fulmarus. These are two species (one in the region) of fairly large petrels with stout pale bills, fairly broad and stiffly held wings, and medium-short, slightly graduated tails. Fulmars inhabit cold temperate waters, often scavenge at fishing boats, and are readily identifiable.

Genus Procellaria. Five species of fairly large petrels that breed in the southern hemisphere, four of which (including the two species recorded in North America) have predominantly blackish plumage and blackish legs and feet, and are sometimes called black petrels.Procellaria bills are pale yellowish overall with well-defined plates and tend to be slightly stouter than shearwater bills; their wings are long and fairly broad, and the tails medium-short and graduated (the toes can project in flight). For species identification note bill size and pattern, overall size (relative to other species), and any white markings on the chin or head.

Genus Bulweria. Two distinctive tropical species (one recorded in the region) of small to medium-sized petrels with stout black bills, long narrow wings, and long, strongly graduated tails usually held closed in a point. Plumage is all-dark with a paler ulnar band, a pattern recalling some large northern storm-petrels.

Family Diomedeidae: Albatrosses

Albatrosses form a well-defined family and differ from other tubenoses in their generally larger size and in having nostril tubes on either side of the bill (see Fig 1). A well-reasoned and widely accepted review by Nunn et al. (1996) identified four recent genera of albatrosses (Fig 17), all of which have occurred in North America: the North Pacific Phoebastria (short-tailed albatrosses) and three southern hemisphere genera: Diomedea (great albatrosses), Thalassarche (mollymawks), and Phoebetria (sooty albatrosses). Moreover, Robertson and Nunn (1998) recommended that 24 albatross species be recognized, a leap from the 12–13 species traditionally recognized and one that has yet to be universally accepted. Although most if not all of these new species are probably valid, it is not always possible to distinguish them at sea.

Genus Phoebastria. Four species of small to medium-large albatrosses with relatively short wings, relatively short tails (the feet project in flight unless pulled in), and generally dull-patterned bills. Ages differ little in three species but strongly in Steller’s Albatross. For species identification check overall color pattern, and bill size and color. Three species occur regularly in North America; one is a vagrant.

Genus Diomedea. A complex of seven taxa (five Wandering Albatrosses and two Royal Albatrosses). These are the largest albatrosses, with huge bodies, very long and narrow wings, relatively short tails (the feet project in flight unless pulled in), and pale pink bills. Ages differ greatly in Wandering Albatrosses, but little in Royals. For species identification check head and body pattern, upperwing pattern, tail pattern, and details of bill pattern and structure. Northern hemisphere records are exceptional and all are of Wandering Albatross taxa, with only three records in the region, all from the Pacific.

Genus Thalassarche. Mollymawks are small to fairly large albatrosses with relatively short wings, relatively long tails (the feet do not project in flight), and brightly patterned bills. Ages differ in appearance; most species attain adult-like plumage aspect in 2–3 years, with fully adult bill pattern taking 4–5 years or longer to develop. For species identification check head and neck pattern, bill color and pattern, underwing pattern, and degree of contrast between hindneck and back. Six taxa of Thallasarche have occurred in North American waters.

Genus Phoebetria. Two species of striking, all-dark, angular albatrosses with long pointed wings and tails and dark bills; one has occurred as a vagrant in North America. Their flight is often spectacular, with higher sailing glides and steeper arcs than other albatrosses, and the wings are typically crooked strongly. Ages differ slightly in appearance. For species identification check overall plumage contrast, head and bill shape, and bill pattern.

Family Hydrobatidae: Northern Storm-Petrels

Storm-petrels appear to be the earliest divergences from the ancestral tubenose lineage and traditionally have been treated as well-defined southern and northern subfamilies. Recent genetic evidence, however, suggests these are better considered distinct families (Nunn & Stanley 1998; see Fig 12), and they are treated here as such. Only 3–4 genera (but 24 or more taxa, at least 19 of which have occurred in North American waters) are recognized among northern storm-petrels.

Genus Oceanodroma. The largest genus of northern storm-petrels, comprising 18+ taxa worldwide (one presumed recently extinct), with 12+ found in the Pacific, 4+ in the Atlantic, and 2 in both oceans. Oceanodroma differ from southern storm-petrels in their longer-armed, more crooked, and relatively narrower wings, and in their shorter legs and smaller feet, which are not habitually used to kick off from the sea surface; the bill, legs, and feet are black. Oceanodroma are medium-sized to large storm-petrels with relatively squared heads and relatively long tails, which are forked or notched; the tarsus is usually shorter than the middle toe, and there is often a strong gray gloss to the fresh dorsal plumage.

Six Oceanodroma taxa are dark-rumped (Ashy, Chapman’s, Markham’s, Tristram’s, Swinhoe’s, and the extralimital Matsudaira’s), as are some Townsend’s [Leach’s]; 9+ taxa are whiterumped (5+ taxa in the Band-rumped complex plus Leach’s, Ainley’s [Leach’s], the extinct Guadalupe, and some Townsend’s), and 3 are handsomely patterned and distinctive (2 subspecies of Fork-tailed, plus Hornby’s). The Band-rumped Storm-Petrel complex may be distinct enough to comprise its own genus, Thalobata (Penhallurick & Wink 2004), and the strikingly distinct Hornby’s Storm-Petrel has yet to be investigated genetically. For at-sea identification note overall size, flight manner (relative to wind conditions), tail length and shape, and details of any white rump patches and pale upperwing bands. Bill size and shape can be helpful for identification, and are best evaluated from photos.

Genus Halocyptena. This includes at least four taxa of the eastern Pacific (Least, Black, and two Wedge-rumped taxa), all of which have at times been subsumed into Oceanodroma but which are distinct enough to warrant separation (Nunn & Stanley 1998). Relative to Oceanodroma, Halocyptena have small, rounded heads, long legs (tarsus usually longer than middle toe), short tails, sooty plumage (with only a slight gray sheen dorsally in fresh plumage), and deep wingbeats. They often feed and raft in fairly tight-knit groups, and patter over food much like Wilson’s or European storm-petrels. Two taxa of Halocyptena (Least and Black) are all-dark, whereas the two Wedge-rumped taxa (which might best be treated as separate species) are white-rumped.

Family Oceanitidae: Southern Storm-Petrels

The southern storm-petrels are outwardly more diverse than are northern storm-petrels, with 17 taxa in 5 genera (5–6 taxa of 3 genera have occurred in North American waters). Relative